There has been a wide variety of sealing rings developed with different cross sectional shapes for use in piston and rod seals for cylinder application, the most common being the O-ring, having a circular cross section. There have also been made sealing rings with other cross sectional shapes such as V-rings, X-rings, square rings and rings having lip seals.
The most commonly used sealing ring is the O-ring, but in making this ring it must be molded, which thereupon provides a flash line around the ring resulting in inconsistency of the sealing surface thereby requiring a greater squeezing force to seal.
Tests show that the best results are obtained when the sealing surfaces of the rings are molded surfaces rather than cut or machined surfaces, particularly when run against a hardened metal surface, but when O-rings or square rings are molded they still have the disadvantages of the flash line.
The disadvantages of a flash line on a molded ring were obviated and the advantages of molded inner and outer sealing surfaces were obtained by the machine disclosed in the Scholin and Lisiecke U.S. Pat. No. 4,030,385 issued June 21, 1977, wherein a sleeve molded of an elastomeric material is cut into a series of rings, each of which is square or rectangular in cross section.
O-rings in dynamic applications have a tendency to roll or twist, and their sealing characteristics are relatively poor compared to those having other cross sectional shapes, such as square. The square ring, on the other hand, even when made in accordance with the teachings of the above mentioned patent, has a very high resistance to sliding forces and has a very high sliding friction. Furthermore, the inconsistency of the manufacture of O-rings causes many problems. For example, excessive flash lines, areas where flash lines are buffed away and mismatching cause strange leakage problems.